The present invention relates to a permeable diaphragm for an electrochemical cell, in particular for a cell for the electrolysis of aqueous solutions of alkali metal halides.
It relates more particularly to a permeable diaphragm, for an electrochemical cell, which is made of a fibrous, organic polymeric material.
It is known to use diaphragms based on organic polymers in the fibrous state in electrochemical cells.
Thus, U.S. Pat. No. 4,036,729, in the name of Patil et al., filed on Apr. 10, 1975 and published on July 19, 1977, relates to a permeable diaphragm which consists of a felt formed, on the perforated cathode of an electrolysis cell, from a dispersion of a fibrous polymeric material in an aqueous medium containing acetone and a surface-active agent.
This known diaphragm exhibits the disadvantage that it requires the incorporation of a surface-active agent in the aqueous medium used for its manufacture, so as to permit adequate dispersion of the polymeric material in this medium. It exhibits the additional disadvantage that it requires the addition, to the fibrous polymeric material, of an additive which can be wetted by the aqueous electrolytes, so that the diaphragm can be sufficiently wetted by these electrolytes. Practice has shown that, in the absence of a wettable additive (such as asbestos fibers, mica, talc or particles of titanium dioxide), the diaphragm is generally too hydrophobic to permit its normal use in electrochemical cells for treating aqueous electrolytes, in particular in cells for the electrolysis of aqueous solutions of alkali metal halides.
Furthermore, the known diaphragm described above exhibits the disadvantageous characteristic that it can only be produced from a very specific and expensive variety of polymic fibers, namely fibers obtained by the melt extrusion of a polymer subjected to an intense shear stress in an auxiliary liquid medium. This characteristic of the known diaphragm has the disadvantageous consequence of increasing its cost.
Japanese Patent Application No. 49/124,302, filed on Apr. 6, 1973 by Mitsubishi Rayon Co., Ltd, describes a process for the manufacture of porous sheets, in accordance with which a fibrous polymeric material, generally a fluorinated polymer, is dispersed in an organic liquid, for example a halogenchydrocarbon, and a felt is separated from the resulting organic suspension.